Optical pickup driving device and optical pickup focus pull-in method

ABSTRACT

In an optical pickup driving apparatus and method, a moving device is controlled when an objective lens is moved toward a recording surface and it is detected that the voltage of the focus error signal has reached a slice level voltage H corresponding to displacement of predetermined magnitude from a reference potential E. The objective lens is moved toward the recording surface by a maximum of an upper limit of a predetermined amount of movement and when the amount of movement of the objective lens reaches the predetermined amount of movement, so as to move the objective lens away from the recording surface. And when it is detected during a period of backward movement of the objective lens, that the voltage of the focus error signal has reached the second slice level voltage H corresponding to displacement of predetermined magnitude from the reference potential E, control of beam spot positioning is performed so as to focus an optical spot.

TECHNICAL FIELD

The present invention relates to an optical pickup driving apparatus andoptical pickup beam spot positioning method, etc., used for an opticalinformation recording/reproducing apparatus (optical informationapparatus) which records/reproduces or erases information stored in anoptical information recording medium such as an optical disk.

BACKGROUND ART

An optical memory technology using an optical disk having a pit-shapedpattern as a high-density, large-volume storage medium has been put topractical use with its application range being expanded to a digitalaudio disk, video disk, document file disk, data file, and so on. Thefunction of successfully recording/reproducing information onto/from anoptical disk through a finely narrowed light beam with a high degree ofreliability can be roughly divided into a condensing function forforming a micro spot narrowed down to a diffraction limit, opticalsystem focus control (focus servo), tracking control and pit signal(information signal) detection.

In recent years, with the advance in optical system design technologiesand shortened wavelengths of a semiconductor laser serving as a lightsource, an optical disk having a higher-density storage capacity than aconventional one is being developed. As an approach to realizinghigher-density storage capacities, a method of increasing numericalaperture (NA) at the side of the optical disk in a condensing opticalsystem which condenses a light beam on the optical disk to a micro levelis under study. The problem in that case is an increase in the amount ofaberration due to an inclination (so-called tilt) of an optical axis.Increasing NA increases the amount of aberration which occurs due totilt. To prevent this, the thickness of the substrate (base material) ofthe optical disk may be reduced.

A compact disk (CD) which can be said to be the first generation opticaldisk uses infrared light (wavelength λ3: 780 nm to 820 nm), an objectivelens having an NA of 0.45 and has a disk base material of 1.2 mm inthickness. The DVD, the second generation, uses red light (wavelengthλ2: 630 nm to 680 nm, standard wavelength 650 nm), an objective lenshaving an NA of 0.6 and a disk base material of 0.6 mm in thickness. Theoptical disk, the third generation, uses blue light (wavelength λ1: 390nm to 415 nm, standard wavelength 405 nm), an objective lens having anNA of 0.85 and a disk base material of 0.1 mm in thickness.

In the present specification, the base material thickness refers to adistance from the plane onto which a light beam impinges in the opticaldisk used as an information recording medium to the informationrecording surface of the optical disk.

Furthermore, for the purpose of realizing a larger-capacity opticaldisk, a disk having a multi-layer structure with two or more recordinglayers is available on the market or under study.

When focus control is applied to such a disk having a multi-layerstructure, or focus control is initially applied from a state in whichfocus servo is not functioning yet, that is, beam spot positioning isperformed, it is important to focus on a desired recording layer inwhich data such as various disk characteristics is written and positionthe beam spot, also for the purpose of shortening a wait time until anoperation is started.

A conventionally proposed beam spot positioning method for a two-layeroptical disk will be explained below.

FIG. 10 is an optical information apparatus which records/reproducesdata onto/from a two-layer optical disk according to a conventionaltechnology. In FIG. 9, a two-layer optical disk 109 is placed on a turntable 182 and rotated by a motor 164 as a rotation system. An opticalhead apparatus 155 is roughly moved to a track in which desiredinformation of the two-layer optical disk 109 exists by a drivingapparatus 151 of the optical head apparatus.

The optical head apparatus 155 also sends a focus error signal ortracking error signal to an electric circuit 153 in accordance with thepositional relationship with the two-layer optical disk 109. In responseto this signal, the electric circuit 153 sends a signal for inching anobjective lens to the optical head apparatus 155. According to thissignal, the optical head apparatus 155 carries out focus control ortracking control on the two-layer optical disk 109 and the optical headapparatus 155 reads, writes or erases information.

FIG. 11 is a flow chart showing a beam spot positioning method for theconventional two-layer optical disk, FIG. 12 illustrates a focus errorsignal waveform and FIG. 13 illustrates a positional relationshipbetween the optical disk and objective lens during beam spot positioningfor the conventional two-layer optical disk. In FIG. 13, referencenumeral 120 denotes a two-layer optical disk whose information recordinglayer has a two-layer structure made up of a first layer 120 b and asecond layer 120 c and 130 denotes an objective lens. Reference numeral170 denotes a focus driving apparatus which drives the objective lens130 in a direction perpendicular to a principal plane including asurface 120 a of the two-layer optical disk 120 and corresponds to thedriving apparatus 151 in FIG. 10. Furthermore, as shown in FIG. 12, thefocus error signal is a signal whose level voltage fluctuates in apositive or negative direction in the vicinity of the recording surfacewith respect to a predetermined reference voltage E according to thedistance from the objective lens 130 and two-layer optical disk 120.

Hereinafter, a case of reproduction of information will be explained asan example according to the flow chart in FIG. 11. When a reproductioncommand on the two-layer optical disk 120 is issued (S101), a laserdiode (not shown) is caused to emit light (S102), then the focus drivingapparatus 170 is driven (S103) and the objective lens 130 is movedwithin a predetermined movement range. The electric circuit 153 turns ONthe focus servo (S104) and monitors the focus error signal of the firstlayer shown by a waveform A in FIG. 12 when the objective lens 130 ismoving. When it is detected that the objective lens has reached point Bin FIG. 11 which is an in-focus point of the first layer 120 b (S105),the focus servo is started (S106) using this focus error signal of thefirst layer 120 b as a control signal, a focus jump is made to point Din FIG. 11 which is the position of the in-focus point of the firstlayer 120 c (S107) (this operation is carried out as a movement of theobjective lens 130 from a state in which the beam spot is positioned atthe first layer 120 b shown in FIG. 13(b) to a state in which the beamspot is positioned at the first layer 120 c shown in FIG. 13(c)), thefocus servo is started (S108) using the focus error signal of the firstlayer 120 c shown by a waveform A in FIG. 12 as a control signal and adata read of the second layer is carried out (S109).

According to the beam spot positioning method for the above describedtwo-layer optical disk, when a data read is performed from the firstlayer 120 c, the focus servo of the first layer 120 b is started first,and then a focus jump is made to start the focus servo for the firstlayer 120 c. For this reason, a time is required until a data read ofthe second layer.

Thus, a beam spot positioning method intended to make data access in ashorter time using a drive apparatus which records/reproduces dataonto/from a two-layer optical disk is disclosed in Japanese PatentLaid-Open No. 9-161284. The structure of the optical informationapparatus which performs beam spot positioning is the same as that ofthe conventional example shown in FIG. 10 and only the control operationis different, and so detailed explanations thereof will be omitted.

FIG. 14 is a flow chart showing a beam spot positioning method for atwo-layer optical disk of the conventional example, FIG. 15 illustratesa focus error signal waveform and FIG. 13 illustrates the positionalrelationship between the two-layer optical disk 120 and objective lens13 during beam spot positioning. Hereinafter, a case of reproduction ofinformation will be explained as an example according to the flow chartin FIG. 14.

When a reproduction command for the two-layer optical disk 120 is issued(S201), the laser diode is caused to emit light (initial state shown inFIG. 12(a)) (S202). Then, the focus driving apparatus 170 moves theobjective lens 130 in a direction perpendicular to the informationrecording surface of the two-layer optical disk 120 within apredetermined range of distance (S203). As the objective lens 130 moves,the electric circuit 153 starts to detect the focus error signal of thefirst layer 120 b shown by a signal waveform A in FIG. 15 (S204), anddetects a period G during which the level voltage of the focus errorsignal is lower than a predetermined focus error signal detection slicelevel voltage F of the first layer 122.

Then, when a time point H at which the focus error signal voltage fallsbelow the first layer focus error signal detection slice level voltage Fis detected again, the focus servo is turned ON (S205).

Next, the focus error signal C of the first layer 120 c indicated by asignal waveform C in FIG. 15 is monitored and if it is detected that theobjective lens 130 has reached the position corresponding to an in-focuspoint D of the first layer 120 c (S206), the focus servo is startedusing the second layer focus error signal C as a control signal (S208)and a data read of the second layer is performed (S209).

However, the above described conventional beam spot positioning methodhas the following problems. That is, as shown in FIG. 15, the focuserror signals of the first layer 120 b and first layer 120 c aredetected by detecting the waveforms A, B, but this detection isperformed by detecting the level voltage at a peak of the waveform or aposition corresponding to predetermined displacement from a focus errorsignal reference voltage E. At this time, if, for example, thereflective index of the first layer 120 c is low and the peak and levelvoltage corresponding to the focus error signal of the first layer 120 ccannot be detected, the objective lens 130 may continue to move insearch of the focus error signal of the second layer, and collide withthe optical disk 120, causing damage to the objective lens 130 oroptical disk 120.

Furthermore, when the reflective index of the first layer 120 b is lowand the focus error signal of the first layer 120 b cannot be detectedfor the same reason as that described above, the focus error signal ofthe first layer 120 c may be mistaken for the focus error signal of thefirst layer and the objective lens 130 may continue to move in search ofthe (inexistent) focus error signal of the first layer 120 c, andfinally collide with the optical disk 120, causing damage to theobjective lens 130 or optical disk 120.

DISCLOSURE OF INVENTION

The present invention has been implemented in view of the abovedescribed problems and it is an object of the present invention toprovide an optical pickup driving apparatus and optical pickup beam spotpositioning method, etc., capable of performing beam spot positioning toa recording layer of the deepest part of a multi-layer disk in a shorttime and reliably.

In order to achieve the above object, the 1^(st) aspect of the presentinvention is an optical pickup driving apparatus for focusing an opticalspot on a single-layer recording surface or a plurality of multi-layeredrecording surfaces of an optical information recording medium,comprising:

moving means of moving an objective lens for focusing said optical spoton said recording surface of said optical information recording mediumin a direction of the optical axis of said optical spot; and

control means of controlling said moving means based on a level voltageof a focus error signal based on reflected light from said optical spot,

wherein said control means controls said moving means so that saidmoving means moves said objective lens toward said recording surface,and when said means detects that the level voltage of said focus errorsignal has reached a first slice level voltage corresponding todisplacement of predetermined magnitude from a reference potential, saidmoving means moves said objective lens toward said recording surface bya maximum of an upper limit of a predetermined amount of movement, andwhen the amount of movement of said objective lens has reached saidpredetermined amount of movement, said moving means moves said objectivelens away from said recording surface, and

when said control means detects that said objective lens has reached asecond slice level voltage corresponding to displacement ofpredetermined magnitude from the reference potential for the period ofsaid backward movement, said control means controls beam spotpositioning so as to focus the optical spot.

The 2^(nd) aspect of the present invention is the optical pickup drivingapparatus according to the 1^(st) aspect of the present invention,wherein when said control means newly detects that the level voltage ofsaid focus error signal has reached a third slice level voltagecorresponding to displacement of predetermined magnitude from saidreference potential before the amount of movement of said objective lensreaches said predetermined amount of movement, said control meanscontrols beam spot positioning so as to focus the optical spot.

The 3^(rd) aspect of the present invention is the optical pickup drivingapparatus according to the 1^(st) or the 2^(nd) aspect of the presentinvention, wherein the level voltage of said focus error signal altersin positive and negative directions with respect to said referencepotential according to the movement of said objective lens, and

said control means detects either a voltage higher or lower than saidreference potential as said first slice level voltage.

The 4^(th) aspect of the present invention is the optical pickup drivingapparatus according to the 3^(rd) aspect of the present invention,wherein said control means uses the voltage higher or lower than saidreference potential as said first slice level voltage, whichever isdetected first.

The 5^(th) aspect of the present invention is the optical pickup drivingapparatus according to the 1^(st) or the 2^(nd) aspect of the presentinvention, wherein the level voltage of said focus error signalfluctuates in positive and negative directions with respect to saidreference potential according to the movement of said objective lens,and

said control means detects both a voltage higher and lower than saidreference potential as said first slice level voltage.

The 6^(th) aspect of the present invention is the optical pickup drivingapparatus according to the 1^(st) or the 2^(nd) aspect of the presentinvention, wherein said control means detects either a voltage higher orlower than said reference potential as said second slice level voltageor said third slice level voltage.

The 7^(th) aspect of the present invention is the optical pickup drivingapparatus according to the 6^(th) aspect of the present invention,wherein said control means uses the voltage higher or lower than saidreference potential as said second slice level voltage or said thirdslice level voltage, whichever is detected first.

The 8^(th) aspect of the present invention is the optical pickup drivingapparatus according to the 1^(st) or the 2^(nd) aspect of the presentinvention, wherein the magnitudes of displacement of said first slicelevel voltage, said second slice level voltage and said third slicelevel voltage from said reference potential are substantially the same.

The 9^(th) aspect of the present invention is the optical pickup drivingapparatus according to the 1^(st) or the 2^(nd) aspect of the presentinvention, wherein the magnitude of displacement of said first slicelevel voltage from said reference potential is greater than themagnitude of displacement of said second slice level voltage and saidthird slice level voltage from said reference potential.

The 10^(th) aspect of the present invention is the optical pickupdriving apparatus according to the 9^(th) aspect of the presentinvention, wherein the magnitudes of displacement of said second slicelevel voltage and said third slice level voltage from said referencepotential are substantially the same.

The 11^(th) aspect of the present invention is the optical pickupdriving apparatus according to the 1^(st) or the 2^(nd) aspect of thepresent invention, wherein said predetermined amount of movement isgiven by a moving distance L from the current position of said opticalpickup when said first slice level voltage is reached and said movingdistance L is defined by:L=d/n×(1+c)  (Formula 1)where d is a maximum value of the distance between said recording layersof said optical information recording medium, n is a refractive index ofsaid optical information recording medium, and c is a sensitivitydifference.

The 12^(th) aspect of the present invention is the optical pickupdriving apparatus according to the 1^(st) or the 2^(nd) aspect of thepresent invention, wherein when said control means detects that thelevel voltage of said focus error signal has reached a fourth slicelevel voltage at which the displacement from said reference potential isgreater than the displacement of said first slice level voltage fromsaid reference potential, said control means controls beam spotpositioning so as to focus said optical spot.

The 13^(th) aspect of the present invention is the optical pickupdriving apparatus according to the 1^(st) or the 2^(nd) aspect of thepresent invention, wherein said control means is formed on an integratedcircuit.

The 14^(th) aspect of the present invention is an optical informationreproducing apparatus provided with means of reading informationrecorded in an optical information recording medium, said reading meansusing the optical pickup driving apparatus according to the 1^(st) orthe 2^(nd) aspect of the present invention.

The 15^(th) aspect of the present invention is an optical informationrecording apparatus provided with recording means of recordinginformation in an optical information recording medium, said recordingmeans using the optical pickup driving apparatus according to the 1^(st)or the 2^(nd) aspect of the present invention.

The 16^(th) aspect of the present invention is an optical informationrecording/reproducing apparatus provided with recording/reproducingmeans of recording and/or reproducing information in/from an opticalinformation recording medium, said recording/reproducing means using theoptical pickup driving apparatus according to the 1^(st) or the 2^(nd)aspect of the present invention.

The 17^(th) aspect of the present invention is an optical pickup beamspot positioning method for focusing an optical spot on a single-layerrecording surface or a plurality of multi-layered recording surfaces ofan optical information recording medium, comprising:

a moving step of moving an objective lens for focusing said optical spoton said recording surface of said optical information recording mediumin a direction of the optical axis of said optical spot; and

a control step of controlling said moving means based on a level voltageof a focus error signal based on reflected light from said optical spot,

wherein said control step controls said moving step so that saidobjective lens moves toward said recording surface, and when it isdetected that the level voltage of said focus error signal has reached afirst slice level voltage corresponding to displacement of predeterminedmagnitude from a reference potential, said objective lens moves towardsaid recording surface by a maximum of an upper limit of a predeterminedamount of movement, and when the amount of movement of said objectivelens has reached said predetermined amount of movement, said objectivelens moves away from said recording surface, and

when it is detected that said objective lens has reached a second slicelevel voltage corresponding to displacement of predetermined magnitudefrom the reference potential for the period of said backward movement,said control step controls beam spot positioning so as to focus theoptical spot.

The 18^(th) aspect of the present invention is the optical pickup beamspot positioning method according to the 17^(th) aspect of the presentinvention, wherein in said control step, when it is newly detected thatthe level voltage of said focus error signal has reached a third slicelevel voltage corresponding to displacement of predetermined magnitudefrom said reference potential before the amount of movement of saidobjective lens reaches said predetermined amount of movement, control ofbeam spot positioning is performed so as to focus the optical spot.

The 19^(th) aspect of the present invention is the optical pickup beamspot positioning method according to the 17^(th) or the 18^(th) aspectof the present invention, wherein the level voltage of said focus errorsignal fluctuates in positive and negative directions with respect tosaid reference potential according to the movement of said objectivelens, and

in said control step, either a voltage higher or lower than saidreference potential is detected as said first slice level voltage.

The 20^(th) aspect of the present invention is the optical pickup beamspot positioning method according to the 19^(th) aspect of the presentinvention, wherein in said control step, the voltage higher or lowerthan said reference potential is used as said first slice level voltage,whichever is detected first.

The 21^(st) aspect of the present invention is the optical pickup beamspot positioning method according to the 17^(th) or the 18^(th) aspectof the present invention, wherein the level voltage of said focus errorsignal fluctuates in positive and negative directions with respect tosaid reference potential according to the movement of said objectivelens, and

in said control step, both a voltage higher and lower than saidreference potential are detected as said first slice level voltage.

The 22^(nd) aspect of the present invention is the optical pickup beamspot positioning method according to the 17^(th) or the 18^(th) aspectof the present invention, wherein in said control step, either a voltagehigher or lower than said reference potential is detected as said secondslice level voltage or said third slice level voltage.

The 23^(rd) aspect of the present invention is the optical pickup beamspot positioning method according to the 22^(nd) aspect of the presentinvention, wherein in said control step, the voltage higher or lowerthan said reference potential is used as said second slice level voltageor said third slice level voltage, whichever is detected first.

The 24^(th) aspect of the present invention is the optical pickup beamspot positioning method according to the 17^(th) or the 18^(th) aspectof the present invention, wherein the magnitudes of displacement of saidfirst slice level voltage, said second slice level voltage and saidthird slice level voltage from said reference potential aresubstantially the same.

The 25^(th) aspect of the present invention is the optical pickup beamspot positioning method according to the 17^(th) or the 18^(th) aspectof the present invention, wherein the magnitude of displacement of saidfirst slice level voltage from said reference potential is greater thanthe magnitudes of displacement of said second slice level voltage andsaid third slice level voltage from said reference potential.

The 26^(th) aspect of the present invention is the optical pickup beamspot positioning method according to the 25^(th) aspect of the presentinvention, wherein the magnitudes of displacement of said second slicelevel voltage and said third slice level voltage from said referencepotential are substantially the same.

The 27^(th) aspect of the present invention is the optical pickup beamspot positioning method according to the 17^(th) or the 18^(th) aspectof the present invention, wherein said predetermined amount of movementis given by a moving distance L from the current position of saidoptical pickup when said first slice level voltage is reached and saidmoving distance L is defined by:L=d/n×(1+c)  (Formula 1)where d is a maximum value of the distance between said recording layersof said optical information recording medium, n is a refractive index ofsaid optical information recording medium, and c is a sensitivitydifference.

The 28^(th) aspect of the present invention is the optical pickup beamspot positioning method according to the 17^(th) or the 18^(th) aspectof the present invention, wherein in said control step, when it isdetected that the level voltage of said focus error signal has reached afourth slice level voltage at which the displacement from said referencepotential is greater than the displacement of said first slice levelvoltage from said reference potential, control of beam spot positioningis performed so as to focus said optical spot.

The 29^(th) aspect of the present invention is a program for causing acomputer to function as control means of controlling said moving meansbased on a level voltage of a focus error signal based on reflectedlight from said optical spot of the optical pickup driving apparatusaccording to the 1^(st) aspect of the present invention.

The 30^(th) aspect of the present invention is a recording mediumcarrying the program according to the 29^(th) aspect of the presentinvention, said recording medium being processable by a computer.

The present invention exerts the notable effect of being able to performbeam spot positioning to a recording layer of the deepest part of amulti-layer disk in a short time and reliably.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a schematic cross-sectional view of an optical informationapparatus according to Embodiments 1 to 6 of the present invention;

FIG. 1(b) is a block diagram of an electric circuit 53 of the opticalinformation apparatus according to Embodiments 1 to 6 of the presentinvention;

FIG. 2 illustrates a flow chart showing a beam spot positioning methodaccording to Embodiment 1 of the present invention;

FIG. 3 illustrates a relationship between a focus error signal and slicelevel voltage according to Embodiments 1 to 4 of the present invention;

FIGS. 4(a), (b), (c) and (d) are schematic cross-sectional views of apositional relationship between an optical disk and objective lens ofeach Embodiment of the present invention;

FIG. 5 illustrates a relationship between a focus error signal and slicelevel voltage according to Embodiments 5 and 6 of the present invention;

FIG. 6 is a schematic perspective view of the structure of a computeraccording to Embodiment 7 of the present invention;

FIG. 7 is a schematic perspective view of the structure of an opticaldisk player and car navigation system according to Embodiment 8 of thepresent invention;

FIG. 8 is a schematic perspective view of the structure of an opticaldisk recorder according to an embodiment of the present invention;

FIG. 9 is a schematic perspective view of the structure of an opticaldisk server according to an embodiment of the present invention;

FIG. 10 is a schematic cross-sectional view of an optical informationapparatus according to a conventional example;

FIG. 11 is a flow chart showing a beam spot positioning method accordingto the conventional example;

FIG. 12 illustrates a focus error signal according to the conventionalexample;

FIGS. 13(a), (b) and (c) are schematic cross-sectional views of apositional relationship between an optical disk and objective lensaccording to the conventional example;

FIG. 14 is a flow chart showing a beam spot positioning method accordingto a conventional example; and

FIG. 15 illustrates a relationship between a focus error signal andslice signal according to the conventional example.

DESCRIPTION OF SYMBOLS

-   9, 121 Optical disk-   131 Objective lens-   171 Focus driving apparatus-   51 Driving apparatus of optical head apparatus-   53 Electric circuit-   55 Optical head apparatus-   61 Output apparatus-   64 Arithmetic unit-   65 Input apparatus-   66 Decoder-   67 Optical information apparatus-   68 Encoder-   69 Input/output terminal-   77 optical disk player (or car navigation system)-   100 Computer-   110 Optical disk recorder-   130 Optical disk server

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the attached drawings, embodiments of the presentinvention will be explained below.

Embodiment 1

FIG. 1(a) is an optical information apparatus according to Embodiment 1of the present invention. In FIG. 1, an optical disk 9 is placed on aturn table 82 and rotated by a motor 64. An optical head apparatus 55 isroughly moved to a track in which desired information of the opticaldisk exists by a driving apparatus 51 of the optical head apparatus.

The optical head apparatus 55 also sends a focus error signal ortracking error signal to an electric circuit 53 in accordance with thepositional relationship with the optical disk 10. In response to thissignal, the electric circuit 53 sends a signal for inching an objectivelens to the optical head apparatus 55. According to this signal, theoptical head apparatus 55 carries out focus control and tracking controlon the optical disk 9 and the optical head apparatus 55 reads, writes orerases information.

Next, FIG. 1(b) schematically shows the interior of the electric circuit53. In the electric circuit 53, a decision circuit 53 a is means ofdetermining whether a focus error signal or tracking error signalobtained from the optical head apparatus 155 has reached a predeterminedlevel voltage or not and a control circuit 53 b is means of performingcontrol to drive various sections of the optical head apparatus 55 andwhen a decision is received from the decision circuit 53 a, the controlcircuit 53 b serves as means of performing control based on thisdecision. Furthermore, a memory 53 c is means of storing the decisionresult of the decision circuit 53 a as a history.

The operation of the optical information apparatus 67 having such astructure will be explained and an embodiment of the beam spotpositioning method for an optical information recording medium of thepresent invention will be explained by taking a case where the opticaldisk 9 is a two-layer disk as an example according to FIGS. 2 to 4. FIG.2 illustrates a flow chart showing a beam spot positioning method for atwo-layer optical disk according to one embodiment of the presentinvention, FIG. 3 illustrates a focus error signal waveform, detected bythe optical head apparatus 55 and FIG. 4 illustrates a positionalrelationship between a two-layer optical disk 121 and objective lens 131during beam spot positioning.

When a command for reproduction from the optical disk is issued from thecontrol circuit 53 b of the electric circuit 53 (S1), a laser diode (notshown) provided in the optical head apparatus 55 is caused to emit light(initial state shown in FIG. 4(a)) (S2). Then, a focus driving apparatus171 is driven (S3) and the objective lens 131 is moved in a directionperpendicular to the information recording surface of the optical disk.At this time, the objective lens 131 is moved by the focus drivingapparatus 171 from a place far from the optical disk 9 to a place closerto the optical disk 9.

At the same time, the decision means 53 b of the electric circuit 53monitors a focus error signal detected when the objective lens 131 ismoving. As shown in FIG. 3, the level voltage of the focus error signalfluctuates in a positive or negative direction in the vicinity of a disksurface 121 a, first layer 121 b and second layer 121 c with respect toa predetermined reference voltage E according to the distances from theobjective lens 131 and optical disk 9. The decision means 53 b detects atime point α at which the level voltage of this focus error signal fallsbelow a predetermined focus error signal detection slice level voltage G(S4) and stores the detection event in the memory 53 c in the electriccircuit 53 as a history. Then, in response to this detection, thecontrol means 53 b sets a limit value (L_(lim)) of an allowable amountof movement of the objective lens 131 (S5).

It is desirable that the absolute value of the difference between thefocus error signal detection slice level voltage G and reference voltageE be ⅓ to ⅔ of the amplitude of a standard focus error signal voltage.This is intended to avoid the focus error signal of the optical disksurface 121 a detected in the state in FIG. 4(a) and indicated by awaveform J in FIG. 3 from being mistaken for the focus error signal ofthe first layer 121 b.

The objective lens 131 continues to approach the optical disk 9 andduring that period of time the decision means 53 b of the electriccircuit 53 determines whether the level voltage of the focus errorsignal has fallen below the focus error signal detection slice levelvoltage G or not in the meantime (S6). When it is detected that thelevel voltage of the focus error signal has fallen below the focus errorsignal detection slice level voltage G again, the focus servo control isturned ON for the first time (S7). At this time, as shown in FIG. 3, thedetection time point is β on the waveform C of the focus error signal ofthe second layer 121 c.

Next, the position D of an in-focus point of the second layer 121 c isdetected (S8), the focus servo is started (S9) using the focus errorsignal of the second layer 122 indicated by a waveform C in FIG. 3 as acontrol signal and a data read is performed (S10). Whether the recordedinformation belongs to the second layer 121 c or not is determined byinformation processing apparatus (not shown), connected to the opticalinformation apparatus, or the electric circuit 53 from the contents ofthe data read through the data read (S13). If the contents are correct,the data read continues (S15) and if incorrect, the control means 53 bperforms control for making a focus jump again (S14) and performs a dataread from the second layer 121 c again (S15). In a focus jump here, thefocus servo is turned OFF, the objective lens 131 is moved closer to theoptical disk 9 and the focus servo is turned ON again when the focuserror signal level has changed by a predetermined value or more withrespect to a reference voltage. At this time, by setting a voltage whosedifference from the reference voltage is smaller than the slice levelvoltage G as a new slice level voltage, a reliable jump is made. In thecase of an optical disk having three or more recording layers, it ispossible to reach a desired recording layer by repeating focus jumps.

On the other hand, even if the objective lens 131 is moved to the limitvalue (L_(lim)) of the allowable amount of movement, if it is notdetermined that the level voltage of the focus error signal has fallenbelow the focus error signal detection slice level voltage G, thecontrol means 53 b of the driving circuit 53 performs control so as tomove the objective lens 131 away from the principal plane of thetwo-layer optical disk 121 from the position of limit value (L_(lim))(S11).

The decision means 53 b of the electric circuit 53 monitors the focuserror signal detected when the objective lens 131 is moving away fromthe disk, determines whether the level voltage falls below the focuserror signal detection slice level voltage G again or not and detectsthe time point at which it falls below the focus error signal detectionslice level voltage G (S12). After the detection, the operations insteps S7 to S15 are executed and a data read is performed from thesecond layer 121 c.

The above described operation will be explained in further detail.According to this embodiment, once a focus error signal is detected, thelimit value (L_(lim)) of the allowable amount of movement is set, themaximum approach position of the objective lens 131 is confirmed as aposition (A) as shown in FIG. 3 and if no new focus error signal isdetected even at the position, the objective lens 131 starts to moveaway from the disk.

The mode of beam spot positioning after the backward movement differs asshown below depending on the detection condition of the focus errorsignal:

(1) When the peaks and level voltage corresponding to the focus errorsignal of the first layer 121 b are detected but the peaks and levelvoltage corresponding to the focus error signal of the second layer 121c cannot be detected:

The decision means 53 b determines in S12 above that the focus errorsignal falls below the focus error signal detection slice level voltageG at a time point γ in the figure, the focus servo is turned ON (S7),operations in S8 to S13 and S15 are performed in that order and a dataread from the second layer 121 c is performed. That is, the optical headapparatus 55 detects the focus error signal of the first layer 121 bonce and then detects the focus error signal of the second layer 121 conce, and can thereby detect an in-focus point D and execute a data readfrom the second layer 121 c appropriately.

(2) When the peaks and level voltage corresponding to the focus errorsignal of the first layer 121 b are not detected but the peaks and levelvoltage corresponding to the focus error signal of the second layer 121c are detected:

In this case, the focus error signal of the second layer 122 is mistakenfor the first layer focus error signal, but the decision means 53 bdetermines in S12 above that the focus error signal has fallen below thefocus error signal detection slice level voltage G at the time point yin the figure, the focus servo is turned ON (S7), operations in S9 toS13 and S15 are performed in that order with the in-focus point Dregarded as a target for an in-focus detection in S8 and a data read isperformed from the second layer 121 c. That is, the optical headapparatus 55 detects the focus error signal of the second layer 121 ctwice, detects an in-focus point D and can execute a data read from thesecond layer 121 c consequently.

As shown above, after a predetermined level voltage signal is detectedas the focus error signal for the first time, a limit value is set inthe amount of movement of the objective lens 131, the objective lens ismoved from there in the opposite direction to detect the focus errorsignal again, and it is thereby possible to avoid collision between theobjective lens 131 and optical disk 121, reliably detect the focus errorsignal a plurality of times and apply the focus servo to the secondlayer directly and in a short time.

The limit value (L_(lim)) of the allowable amount of movement of theobjective lens 131 can be set to an arbitrary distance from the positionat which the optical head apparatus 55 starts to operate to the positionat which the optical lens 131 contacts the surface of the optical disk121 in principle, but it is desirable to omit unnecessary movement forspeedy beam spot positioning.

Thus, according to this embodiment, a moving distance L from the currentposition at the time of the first detection of the focus error signal asa starting point is determined, the objective lens is moved closer tothe disk by this moving distance L and then the objective lens is movedaway from the disk. That is, in the two-layer optical disk 121, themoving distance L is set to a value obtained by dividing a maximum valued of the distance between two layers (between the first layer 121 b andsecond layer 121 c) by a refractive index n of the substrate material ofthe optical disk 121 and further adding a sensitivity difference c ofthe optical head apparatus 55 thereto. That is, the moving distance Lfrom the first focus error signal detection point is defined using theseparameters as:L=d/n×(1+c)  (Formula 1)where c is approximately 0.1 to 0.3.

Furthermore, the distance between the surface of the objective lens 131close to the disk when focus is achieved on the first layer 121 b andthe surface of the optical disk 121 is called a “working distance” (WD).By setting WD>L, it is possible to obtain the effect that the objectivelens does not collide with the disk when the objective lens is beingmoved by a certain amount L, and therefore it is desirable to set WD>L.

In this way, it is possible to determine whether or not to achieve asecond detection of the focus error signal within a period ofapproaching movement of the shortest distance from the time of the firstdetection of the focus error signal in S4 and realize speedy beam spotpositioning.

In the foregoing explanations, the embodiment of a two-layer disk hasbeen shown, but in the case of a multi-layer disk having three or morelayers, it is also possible to realize speedy beam spot positioning tothe recording layer in the deepest part through the same operation asthat described above as far as the recording surface subject to beamspot positioning is in the deepest part of the optical disk. At thistime, the moving distance L can be defined as follows. That is, L can beset to a value obtained by dividing the maximum value d of the distancesbetween four layers by a refractive index n of the optical disk andadding a sensitivity difference c of the driving apparatus 51 thereto.That is, in the same way as the above expression, the followingexpression can be set:L=d/n×(1+c)  (Formula 1)

Assuming the number of recording layers is N_(L), by turning ON thefocus servo control immediately after detecting that the focus errorsignal exceeds the slice level voltage g, (N_(L)−1) times when theobjective lens is being moved by a certain amount L, it is also possibleto realize beam spot positioning more speedily.

That is, in the case where the optical disk is a multi-layer disk havingthree or more layers, after a focus error signal is detected, theobjective lens is brought closer to the optical disk by a certain amountand if the next focus error signal can be detected, the objective lensis sent further and if not, the objective lens is moved in the oppositedirection and beam spot positioning is performed using the focus errorsignal detected immediately before. By determining this number of times,it is possible to perform direct beam spot positioning to a desiredrecording layer and avoid collision between the objective lens andoptical disk.

Embodiment 2

In Embodiment 1 above, the level voltage G which is lower than thereference voltage E is used as the slice level voltage used to detect afocus error signal of each recording layer, but the slice level voltageis not limited to this.

As another example of the slice level voltage, the decision means 53 acan also use a slice level voltage H which is higher than the referencevoltage E to detect a time point at which a focus error signal beingmonitored exceeds this slice level voltage H for the first time as thetime of detection of the first focus error signal in S4. In this case,as shown in FIG. 3, the time of the first detection of the focus errorsignal and the limit value (L_(lim)) of the allowable amount of movementof the objective lens 131 in S5 are set at a time point δ in the figure.Furthermore, the time at which the objective lens 131 detects the focuserror signal for the second time is a time point ε in the figure.

Furthermore, as another example of the slice level voltage, it ispossible to use the above described slice level voltages G and H in nospecial order at the first detection of the focus error signal and thesecond detection of the focus error signal respectively. The operationin this case will be as follows:

(1) The slice level voltage G is used for the first detection of thefocus error signal and the slice level voltage H is used for the seconddetection of the focus error signal.

At this time, as shown in FIG. 3, the time point of the first detectionof the focus error signal and the limit value (L_(lim)) of the allowableamount of movement of the objective lens 131 in S5 are set at time pointα in the figure, while the time point for the second detection of thefocus error signal when there is no backward movement caused by thesetting of the limit value (L_(lim)) of the allowable amount of movementof the objective lens 131 is a time point ε in the figure. Furthermore,the time point for the second detection of the focus error signal whenthere is backward movement is a time point ζ in the figure.

In this way, using the slice level voltages can shorten the time betweenthe first detection of the focus error signal and second detection ofthe focus error signal and thereby realize speedy beam spot positioning.

(2) Next, the slice level voltage H is used for the first detection ofthe focus error signal and the slice level voltage G is used for thesecond detection of the focus error signal.

At this time, as shown in FIG. 3, the time point of the first detectionof the focus error signal and the limit value (L_(lim)) of the allowableamount of movement of the objective lens 131 in S5 are set at the timepoint δ in the figure, while the time point for the second detection ofthe focus error signal when there is no backward movement caused by thesetting of the limit value (L_(lim)) of the allowable amount of movementof the objective lens 131 is the time point β in the figure.Furthermore, the time point for the second detection of the focus errorsignal when there is backward movement is the time point γ in thefigure.

Embodiment 3

Furthermore, as a further example of the slice level voltage, it ispossible to use the above described slice level voltages G and H in nospecial order for the backward movement caused by the setting of thelimit value (L_(lim)) of the allowable amount of movement andapproaching movement before the backward movement started respectively.The operation in this case will be as follows:

(1) The slice level voltage G is used to detect a focus error signalduring approaching movement and the slice level voltage H is used todetect a focus error signal during backward movement.

At this time, as shown in FIG. 3, the time point of the first detectionof the focus error signal (and the limit value (L_(lim)) of theallowable amount of movement of the objective lens 131 in S5) is set atthe time point a in the figure, and the time point of the seconddetection of the focus error signal when there is no backward movementcaused by the setting of the limit value (L_(lim)) of the allowableamount of movement of the objective lens 131 is the time point β in thefigure, while the time point of the second detection of the focus errorsignal when there is backward movement is the time point ζ in thefigure.

(2) The slice level voltage H is used to detect a focus error signalduring approaching movement and the slice level voltage G is used todetect a focus error signal during backward movement.

At this time, as shown in FIG. 3, the time point of the first detectionof the focus error signal (and the limit value (L_(lim)) of theallowable amount of movement of the objective lens 131 in S5) is set atthe time point δ in the figure, and the time point of the seconddetection of the focus error signal when there is no backward movementcaused by the setting of the limit value (L_(lim)) of the allowableamount of movement of the objective lens 131 is the time point ε in thefigure, while the time point of the second detection of the focus errorsignal when there is backward movement is the time point γ in thefigure. In this way, using the slice level voltages can shorten the timebetween the first detection of the focus error signal and seconddetection of the focus error signal when backward movement is necessaryand thereby realize speedy beam spot positioning.

Embodiments 2, 3 assume that each of the slice level voltages H, G isused once for detection of the focus error signal and have enumeratedtheir combinations, but it is desirable to give priority to theshortening of time required for detection when a beam spot positioningoperation is actually performed. In the example shown in FIG. 3, theearliest one of the time points of the first detection of the focuserror signal is the time point δ, that of the time point of the seconddetection of the focus error signal is the time point ε duringapproaching movement and time point γ during backward movement, andtherefore as far as the slice level voltage is concerned, it is mostefficient to perform the detection operation with the setting (2) inEmbodiment 2.

Embodiment 4

As a still further example of the slice level voltage, it is possible touse both the above described slice level voltages G and H for the firstdetection of the focus error signal and second detection of the focuserror signal. The operation in this case will be as follows. That is,the time point of the first detection of the focus error signal and thelimit value (L_(lim)) of the allowable amount of movement of theobjective lens 131 in S5 are set at the time point α after checking thetime point δ in the figure and the time point of the second detection ofthe focus error signal when there is no backward movement caused by thesetting of the limit value (L_(lim)) of the allowable amount of movementof the objective lens 131 is further set at the time point γ after thetime point ε in the figure was confirmed. Furthermore, the time point ofthe second detection of the focus error signal when there is backwardmovement is further set at the time point ζ after the time point γ inthe figure was confirmed.

In this case, by detecting a focus error signal whose potential withrespect to the reference voltage E is fluctuating in positive andnegative directions from both the positive and negative sides, it ispossible to reduce the possibility that errors caused by damage orspoiling etc., on the optical disk 9 may be mistaken for focus errorsignals and realize reliable beam spot positioning.

Embodiment 5

As a still further example of the slice level voltage, it is possible todifferentiate the magnitude of the above described slice level voltagebetween backward movement caused by the setting of a limit value(L_(lim)) of the allowable amount of movement and approaching movementbefore the backward movement started. That is, it is possible to causethe magnitude of the slice level voltage used for the detection of thefocus error signal during backward movement to be smaller than themagnitude of the slice level voltage used for the first detection of thefocus error signal. As shown in FIG. 4, when the focus error signal isdetected using the slice level voltage H, the first detection of thefocus error signal is performed at time point δ. The second detection ofthe focus error signal should be performed originally at the time pointε, but if some trouble occurs for some reason, after the objective lens131 is moved to the point (A) based on the limit value (L_(lim)) of theallowable amount of movement set at the first detection of the focuserror signal, the objective lens 131 is moved away from the point (A) inthe opposite direction and an attempt to detect the focus error signalis made again during the backward movement.

When the focus error signal is detected during backward movement, if theslice level voltage H is used in the same way as the first detection,the detection is performed at the time point ζ shown in FIG. 4, but whenthe failure of approaching movement is attributable to a reduction ofthe reflective index of the second layer 121 c, for example, the levelvoltage of the focus error signal itself has not reached the slice levelvoltage H as shown by the dotted line in FIG. 4, and therefore the focuserror signal cannot be detected even during backward movement.

Thus, according to this embodiment, when the objective lens 131 startsbackward movement, the decision means 53 a sets the slice level voltageto a voltage H_(low) which is lower than the slice level voltage H withrespect to the reference voltage E, determines the time point at whichthe focus error signal being monitored exceeds this new H_(low), anddetects an in-focus point using the focus error signal at this time. Forthe focus error signal of the second layer 121 b, a time point ζ′ shownin the figure is the decision point.

Thus, this embodiment causes the magnitude of the slice level voltageduring backward movement to be smaller than that during approachingmovement, and can thereby detect the focus error signal of the secondlayer more reliably and perform speedy beam spot positioning.

In the explanations so far, the slice level voltage H_(low) which islower than the slice level voltage H with respect to the referencevoltage E is used, but when the slice level G is used for the firstdetection of the focus error signal, a slice level voltage G_(high) (notshown) which is higher than the slice level voltage G with respect tothe reference voltage E can be used. In short, it is sufficient to set aslice level voltage which has smaller displacement than the displacementof the slice level voltage used for the first detection from thereference voltage. Furthermore, combined with Embodiments 2 to 4, whenboth slice level voltages G and H are used separately or together, it ispossible to use the slice level voltages H_(low), and G_(high) for thesecond detection of the focus error signal during backward movement orapproaching movement respectively.

In the explanations above, the slice level voltage H_(low) is used todetect a focus error signal during backward movement, but the slicelevel voltage H_(low) can also be used for the second detection of thefocus error signal during approaching movement. In this case, the focuserror signal can be detected at a time point ε′ in FIG. 4, in which casebackward movement is not necessary and beam spot positioning can befurther sped up. Furthermore, as far as the displacement is smaller thanthe displacement of the slice level voltage from the reference potentialused for the first detection of the focus error signal, the displacementfrom the reference voltage E can be differentiated between approachingmovement and backward movement in the second detection of the focuserror signal.

Embodiment 6

When a single-layer disk having only one recording layer is used as theoptical disk 9, speedy beam spot positioning may be realized as follows.

That is, in the case of a single-layer disk, compared to a multi-layerdisk, the reflective index of the recording layer is larger and thelevel voltage of the focus error signal is also larger, and thereforethe decision means 53 a sets H_(high) at which the displacement from thereference potential E is higher than the slice level voltage H used forthe first detection of the focus error signal, and after the focus errorsignal being monitored reaches the slice level voltage H and a movementlimit is set, if it is detected that this slice level voltage H_(high)has been reached, the decision means 53 a detects an in-focus point. InFIG. 4, that slice level voltage H_(high) has been reached is detectedat the time point δ′ and beam spot positioning is thereby performed tothe in-focus point B of the first layer.

In the above described explanations, the slice level voltage H is usedto detect the focus error signal, and therefore H_(high) which is higherthan the slice level voltage H is set, but it is also possible to set alevel voltage G_(low) (not shown) which is lower than the slice levelvoltage G with respect to the reference voltage E as the onecorresponding to the case where the slice level voltage G is used todetect a focus error signal. That is, it is possible to set the levelvoltage of the focus error signal to a slice level voltage such that thedisplacement from the reference potential is greater than thedisplacement of the slice level voltage used for the first detection ofthe focus error signal from the reference potential and detect that thisslice level voltage has been reached.

Furthermore, it is also possible to combine this embodiment withEmbodiment 4 to set and detect both the slice level voltages H_(high)and G_(low).

Embodiment 7

As examples of the optical information recording apparatus, opticalinformation reproducing apparatus and optical information recordingapparatus, an embodiment of a computer, etc., provided with the opticalinformation apparatus 67 described in Embodiments 1 to 6 will be shownbelow.

A computer, optical disk player or optical disk recorder provided withthe optical information apparatus of the above described embodiment oradopting the above described recording/reproducing method can performbeam spot positioning to a desired recording layer of a multilayeroptical disk in a short time and prevent collision between the objectivelens and optical disk, and can thereby realize a system with excellentoperability with a shorter wait time before starting operation of theoptical disk.

In FIG. 6, a computer 100 is constructed of the optical informationapparatus 67 according to Embodiments 1 to 6, an input apparatus 65implemented by a keyboard, mouse or touch panel for inputtinginformation, an arithmetic unit 64 implemented by a central processingunit (CPU), etc., which performs operations based on information inputfrom the input apparatus 65 and information read from the opticalinformation apparatus 67 and an output apparatus 61 implemented by aCRT, liquid crystal display apparatus or printer which displaysinformation such as operation results of the arithmetic unit 64.

Embodiment 8

An embodiment of an optical disk player provided with the opticalinformation apparatus 67 described in Embodiments 1 to 6 is shown inFIG. 7.

In FIG. 7, an optical disk player 77 is constructed of the opticalinformation apparatus 67 according to Embodiments 1 to 6 and a decoder66 as an apparatus which converts an information signal obtained fromthe optical information apparatus 67 to an image. Furthermore, thisstructure can also be used as a car navigation system. Furthermore, theapparatus of the present invention may also be used in a mode providedwith a display apparatus 120 such as a liquid crystal monitor.

Embodiment 9

An embodiment of an optical disk recorder provided with the opticalinformation apparatus described in Embodiments 1 to 6 will be shownbelow.

Embodiment 9 will be explained using FIG. 8. In FIG. 8, an optical diskrecorder is constructed of the optical information apparatus 67according to Embodiment 7 and an encoder 68 as an apparatus whichconverts image information to information which is recorded in anoptical disk by the optical information apparatus 67. Preferably by alsoincluding a decoder 66 as an apparatus which converts an informationsignal obtained from the optical information apparatus 67 to an image,it is also possible to reproduce an already recorded portion. Theoptical disk recorder may also include an output apparatus 61 which isimplemented as a CRT, liquid crystal display apparatus or printer whichdisplays information.

Embodiment 10

Embodiment 10 will be explained using FIG. 9. In FIG. 9, an opticalinformation apparatus 67 is the optical information apparatus describedin Embodiments 1 to 6. Furthermore, an input/output terminal 69 is awired or wireless input/output terminal which inputs information to berecorded in the optical information apparatus 67 or outputs informationread by the optical information apparatus 67 to the outside. This allowsthe present invention to be used as an information server (optical diskserver) which exchanges information with a network, that is, a pluralityof devices, for example, a computer, telephone, television tuner, etc.,and which is shared by the plurality of devices. This allows opticaldisks of different types to be stably recorded or reproduced, thushaving the effect of being applicable to a wide range of applications.It is also possible to include an output apparatus 61 which isimplemented as a CRT, liquid crystal display apparatus or printer whichdisplays information.

Furthermore, by also including a changer 131 which loads/unloads aplurality of optical disks into/from the optical information apparatus67, it is possible to produce the effect of recording/storing a largevolume of information.

Embodiments 7 to 10 have shown the output apparatus 61 and liquidcrystal monitor 120 in FIGS. 6 to 9, but it is also possible to adopt astructure provided with only output terminals for connections with thesedevices. In this case, it is possible to provide a mode in which theoutput apparatus 61 and liquid crystal monitor 120 are not provided, butthese devices are made available separately as required. Furthermore,FIG. 7 and FIG. 8 show no input apparatus, but it is also possible toadopt a mode provided with an input apparatus such as a keyboard, touchpanel, mouse, remote control apparatus, etc. On the contrary, inEmbodiments 7 to 10 above, it is also possible to adopt a mode in whichthe input apparatus is provided separately and only input terminals forconnections with the input apparatus are included.

In the above described embodiments, the optical head apparatus 55including the focus driving apparatus 171 corresponds to the movingmeans of the present invention, the objective lens 131 corresponds tothe objective lens of the present invention and the electric circuit 53corresponds to the control means of the present invention. Furthermore,the slice level voltage such as the slice level voltage H, G used forthe first detection of a focus error signal in S4 corresponds to thefirst slice level voltage of the present invention, the slice levelvoltage such as the slice level voltage H, G used for the seconddetection of a focus error signal during approaching movement in S6corresponds to the second slice level voltage of the present invention,the slice level voltage such as the slice level voltage H, G used forthe second detection of a focus error signal during backward movementcorresponds to the third slice level voltage of the present invention.Furthermore, the slice level voltage such as slice level voltageH_(high), G_(low) used in Embodiment 4 corresponds to the fourth slicelevel voltage of the present invention. Furthermore, the personalcomputer 100, optical disk recorder 110 and optical disk server 130provided with the optical information apparatus 67 correspond to theoptical information reproducing apparatus, optical information recordingapparatus and optical information recording/reproducing apparatus, andthe optical disk player 77 corresponds to the optical informationreproducing apparatus of the present invention.

Furthermore, in the above described embodiments, using an integratedcircuit such as a semiconductor integrated circuit for the electriccircuit 53 can reduce the size of the apparatus, provide lower power,and improve reliability.

Furthermore, the program according to the present invention is a programfor causing a computer to execute the functions of the whole or part ofthe above described optical pickup driving apparatus of the presentinvention and can be a program which operates in cooperation with thecomputer.

Furthermore, the present invention may also be a medium carrying aprogram for causing a computer to execute the functions of the whole orpart of the above described optical pickup driving apparatus of thepresent invention and can be a computer-readable medium, the programread from which executes the above described functions in cooperationwith the computer.

The above described “part of the means” means some of a plurality ofmeans or means part of the function of one means.

Furthermore, “some apparatuses” of the present invention means some of aplurality of apparatuses or means some means of one apparatus or meanspart of the function of one means.

Furthermore, a computer-readable recording medium which records theprogram of the present invention is also included in the presentinvention.

Furthermore, a mode of use of the program of the present invention mayalso be a mode in which the program is recorded in a computer-readablerecording medium and operates in cooperation with the computer.

Furthermore, a mode of use of the program of the present invention mayalso be a mode in which the program is transmitted through atransmission medium, read by a computer and operates in cooperation withthe computer.

Furthermore, the data structure of the present invention includes adatabase, data format, data table, data list or data type, etc.

Furthermore, the recording medium includes a ROM, etc., and thetransmission medium includes a transmission mechanism such as theInternet, light, radio wave, sound wave, etc.

Furthermore, the above described computer of the present invention isnot limited to pure hardware such as a CPU, but may also includefirmware, OS or peripheral devices.

As described above, the structure of the present invention may beimplemented by software or implemented by hardware.

INDUSTRIAL APPLICABILITY

The present invention exerts notable effects as an optical pickupdriving apparatus and optical pickup beam spot positioning method, etc.,that can perform beam spot positioning to a recording layer in thedeepest part of a multi-layer disk in a short time and in a reliablemanner, and is applicable to wide industrial fields including audio,video, and computer as a large-volume, removable, randomly accessibleinformation storage apparatus such as various devices using an opticalinformation apparatus which records/reproduces a single-layer ormulti-layer optical disk, for example, video reproducing machine, videorecorder, car AV system, audio device, storage apparatus for a computer,home server, business data backup apparatus, etc., and the range ofindustrial applicability thereof is wide and large.

1. An optical pickup driving apparatus for focusing an optical spot on asingle-layer recording surface or a plurality of multi-layered recordingsurfaces of an optical information recording medium, comprising: movingmeans of moving an objective lens for focusing said optical spot on saidrecording surface of said optical information recording medium in adirection of the optical axis of said optical spot; and control means ofcontrolling said moving means based on a voltage of a focus error signalbased on reflected light from said optical spot, wherein said controlmeans controls said moving means so that said moving means moves saidobjective lens toward said recording surface, and when said controlmeans detects that the voltage of said focus error signal has reached afirst slice level voltage corresponding to displacement of predeterminedmagnitude from a reference potential, said moving means moves saidobjective lens toward said recording surface by a maximum of an upperlimit of a predetermined amount of movement, and when the amount ofmovement of said objective lens has reached said predetermined amount ofmovement, said moving means moves said objective lens away from saidrecording surface, and when said control means detects that saidobjective lens has reached a second slice level voltage corresponding todisplacement of predetermined magnitude from the reference potential forthe period of said backward movement, said control means controls beamspot positioning so as to focus the optical spot.
 2. The optical pickupdriving apparatus according to claim 1, wherein when said control meansnewly detects that the voltage of said focus error signal has reached athird slice level voltage corresponding to displacement of predeterminedmagnitude from said reference potential before the amount of movement ofsaid objective lens reaches said predetermined amount of movement, saidcontrol means controls beam spot positioning so as to focus the opticalspot.
 3. The optical pickup driving apparatus according to claim 1 or 2,wherein the voltage of said focus error signal alters in positive andnegative directions with respect to said reference potential accordingto the movement of said objective lens, and said control means detectseither a voltage higher or lower than said reference potential as saidfirst slice level voltage.
 4. The optical pickup driving apparatusaccording to claim 3, wherein said control means uses the voltage higheror lower than said reference potential as said first slice levelvoltage, whichever is detected first.
 5. The optical pickup drivingapparatus according to claim 1 or 2, wherein the voltage of said focuserror signal fluctuates in positive and negative directions with respectto said reference potential according to the movement of said objectivelens, and said control means detects both a voltage higher and lowerthan said reference potential as said first slice level voltage.
 6. Theoptical pickup driving apparatus according to claim 1 or 2, wherein saidcontrol means detects either a voltage higher or lower than saidreference potential as said second slice level voltage or said thirdslice level voltage.
 7. The optical pickup driving apparatus accordingto claim 6, wherein said control means uses the voltage higher or lowerthan said reference potential as said second slice level voltage or saidthird slice level voltage, whichever is detected first.
 8. The opticalpickup driving apparatus according to claim 1 or 2, wherein themagnitudes of displacement of said first slice level voltage, saidsecond slice level voltage and said third slice level voltage from saidreference potential are substantially the same.
 9. The optical pickupdriving apparatus according to claim 1 or 2, wherein the magnitude ofdisplacement of said first slice level voltage from said referencepotential is greater than the magnitude of displacement of said secondslice level voltage and said third slice level voltage from saidreference potential.
 10. The optical pickup driving apparatus accordingto claim 9, wherein the magnitudes of displacement of said second slicelevel voltage and said third slice level voltage from said referencepotential are substantially the same.
 11. The optical pickup drivingapparatus according to claim 1 or 2, wherein said predetermined amountof movement is given by a moving distance L from the current position ofsaid optical pickup when said first slice level voltage is reached andsaid moving distance L is defined by:L=d/n×(1+c)  (Formula 1) where d is a maximum value of the distancebetween said recording layers of said optical information recordingmedium, n is a refractive index of said optical information recordingmedium, and c is a sensitivity difference.
 12. The optical pickupdriving apparatus according to claim 1 or 2, wherein when said controlmeans detects that the voltage of said focus error signal has reached afourth slice level voltage at which the displacement from said referencepotential is greater than the displacement of said first slice levelvoltage from said reference potential, said control means controls beamspot positioning so as to focus said optical spot.
 13. The opticalpickup driving apparatus according to claim 1 or 2, wherein said controlmeans is formed on an integrated circuit.
 14. An optical informationreproducing apparatus provided with means of reading informationrecorded in an optical information recording medium, said reading meansusing the optical pickup driving apparatus according to claim 1 or 2.15. An optical information recording apparatus provided with recordingmeans of recording information in an optical information recordingmedium, said recording means using the optical pickup driving apparatusaccording to claim 1 or
 2. 16. An optical informationrecording/reproducing apparatus provided with recording/reproducingmeans of recording and/or reproducing information in/from an opticalinformation recording medium, said recording/reproducing means using theoptical pickup driving apparatus according to claim 1 or
 2. 17. Anoptical pickup beam spot positioning method for focusing an optical spoton a single-layer recording surface or a plurality of multi-layeredrecording surfaces of an optical information recording medium,comprising: a moving step of moving an objective lens for focusing saidoptical spot on said recording surface of said optical informationrecording medium in a direction of the optical axis of said opticalspot; and a control step of controlling said moving means based on avoltage of a focus error signal based on reflected light from saidoptical spot, wherein said control step controls said moving step sothat said objective lens moves toward said recording surface, and whenit is detected that the voltage of said focus error signal has reached afirst slice level voltage corresponding to displacement of predeterminedmagnitude from a reference potential, said objective lens moves towardsaid recording surface by a maximum of an upper limit of a predeterminedamount of movement, and when the amount of movement of said objectivelens has reached said predetermined amount of movement, said objectivelens moves away from said recording surface, and when it is detectedthat said objective lens has reached a second slice level voltagecorresponding to displacement of predetermined magnitude from thereference potential for the period of said backward movement, saidcontrol step controls beam spot positioning so as to focus the opticalspot.
 18. The optical pickup beam spot positioning method according toclaim 17, wherein in said control step, when it is newly detected thatthe voltage of said focus error signal has reached a third slice levelvoltage corresponding to displacement of predetermined magnitude fromsaid reference potential before the amount of movement of said objectivelens reaches said predetermined amount of movement, control of beam spotpositioning is performed so as to focus the optical spot.
 19. Theoptical pickup beam spot positioning method according to claim 17 or 18,wherein the voltage of said focus error signal fluctuates in positiveand negative directions with respect to said reference potentialaccording to the movement of said objective lens, and in said controlstep, either a voltage higher or lower than said reference potential isdetected as said first slice level voltage.
 20. The optical pickup beamspot positioning method according to claim 19, wherein in said controlstep, the voltage higher or lower than said reference potential is usedas said first slice level voltage, whichever is detected first.
 21. Theoptical pickup beam spot positioning method according to claim 17 or 18,wherein the voltage of said focus error signal fluctuates in positiveand negative directions with respect to said reference potentialaccording to the movement of said objective lens, and in said controlstep, both a voltage higher and lower than said reference potential aredetected as said first slice level voltage.
 22. The optical pickup beamspot positioning method according to claim 17 or 18, wherein in saidcontrol step, either a voltage higher or lower than said referencepotential is detected as said second slice level voltage or said thirdslice level voltage.
 23. The optical pickup beam spot positioning methodaccording to claim 22, wherein in said control step, the voltage higheror lower than said reference potential is used as said second slicelevel voltage or said third slice level voltage, whichever is detectedfirst.
 24. The optical pickup beam spot positioning method according toclaim 17 or 18, wherein the magnitudes of displacement of said firstslice level voltage, said second slice level voltage and said thirdslice level voltage from said reference potential are substantially thesame.
 25. The optical pickup beam spot positioning method according toclaim 17 or 18, wherein the magnitude of displacement of said firstslice level voltage from said reference potential is greater than themagnitudes of displacement of said second slice level voltage and saidthird slice level voltage from said reference potential.
 26. The opticalpickup beam spot positioning method according to claim 25, wherein themagnitudes of displacement of said second slice level voltage and saidthird slice level voltage from said reference potential aresubstantially the same.
 27. The optical pickup beam spot positioningmethod according to claim 17 or 18, wherein said predetermined amount ofmovement is given by a moving distance L from the current position ofsaid optical pickup when said first slice level voltage is reached andsaid moving distance L is defined by:L=d/n×(1+c)  (Formula 1) where d is a maximum value of the distancebetween said recording layers of said optical information recordingmedium, n is a refractive index of said optical information recordingmedium, and c is a sensitivity difference.
 28. The optical pickup beamspot positioning method according to claim 17 or 18, wherein in saidcontrol step, when it is detected that the voltage of said focus errorsignal has reached a fourth slice level voltage at which thedisplacement from said reference potential is greater than thedisplacement of said first slice level voltage from said referencepotential, control of beam spot positioning is performed so as to focussaid optical spot.
 29. A program for causing a computer to function ascontrol means of controlling said moving means based on a voltage of afocus error signal based on reflected light from said optical spot ofthe optical pickup driving apparatus according to claim
 1. 30. Arecording medium carrying the program according to claim 29, saidrecording medium being processable by a computer.